Add formatting option to customise legend position

[Bergam0t]

At the moment having the legend on the right is quite nice when the plot is large, but it takes up a lot of space if you try to put two plots side by side on a standard PBI page.

Add a dropdown to the formatting menu to allow you to choose between a couple of positions - top, bottom, left, right, off?

[Bergam0t]

Done in this commit

Added options for right, bottom, off.

More options could be added if needed.

Bottom is a bit temperamental - known plotly issue here